None.
The present invention relates to a multilayer device which can be used to indicate the amount of exposure to sunlight. More specifically, the present invention relates to a multilayer sunlight dosage indicator comprising: (a) an indicator layer comprising a sunlight-sensitive ink, wherein the ink undergoes a color change upon exposure to a known amount of sunlight; and (b) an overlayer comprising an amount of at least one UV absorber. The present invention also relates to a method for indicating the amount of exposure to sunlight. Further, the present invention relates to a method for adjusting the sensitivity of the indicator by adding UV absorbing materials to the overlayer.
Sunlight contains ultraviolet (UV) radiation. In small amounts, UV radiation is necessary and healthy. For example, it aids in the production of vitamin D. Excessive exposure to UV radiation, however, can have harmful effects on health, including sunburn. In view of this, various devices have been developed to indicate and measure UV exposure, so that excessive exposure can be avoided.
U.S. Pat. No. 4,705,046 discloses a device for the qualitative measurement of UV radiation received by the skin. When the device is exposed to sunlight, a comparison of the color density of a photochromic material and a reference dye allows a qualitative determination of the amount of exposure to UV radiation.
U.S. Pat. No. 5,581,090 discloses an ultraviolet detector based on a photochromic composition that changes color upon exposure to UV rays. The photochromic material is dissolved in a solvent and applied to an article such as a watch or credit card.
U.S. Pat. No. 5,914,197 teaches an UV active wristband which changes color reversibly from clear to any visible color when exposed to a UV source.
U.S. Pat. No. 5,986,273 discloses an ultraviolet radiation sensor that may be worn on the skin. The sensor includes a transparent membrane, an adhesive, and an indicator that reversibly alters its color when exposed to UV radiation.
These prior art devices are able to indicate a fairly narrow range of UV exposure, but the amount of UV exposure safely tolerated by humans varies over a wide range. Furthermore, the color change in the prior art devices is reversible. This is, once the user moves out of exposure the devices reverse and, upon reexposure, will again begin their measurement. Therefore, they cannot be used to measure cumulative UV exposure.
Also, skin type is an important factor in determining how much UV exposure is safe and how much is detrimental. Sensitive skin burns easily and more severely at lower levels of UV exposure than normal skin. Fair-skinned people require only about 15-60 minutes of midday summer sunshine to induce an erythemal reaction. Thus, a sunlight dosage indicator that changes color after about 15-60 minutes is needed for use by fair-skinned people.
On the other hand, people with normal skin may require 1 to 2 hours of exposure before an erythemal reaction is observed so that sunlight dosage indicator with a response time of 1 to 2 hours is needed for use by people with normal skin. An indicator with an even longer response time is needed for people with moderately pigmented skin. A sunlight dosage indicator that can be customized for sensitive, normal, or other skin type would therefore be advantageous to accommodate usage by persons having a wide range of sensivitity.
Additionally, because people often apply sunscreen to minimize the skin""s exposure to UV radiation, a sunlight dosage indicator should complement the use of sunscreen by tolerating a coating of sunscreen, while still accurately indicating the UV light dosage to the protected skin.
As noted then, the sunlight dosage indicator should provide a cumulative measure of UV exposure; should also provide an improvement in abrasion resistance, water resistance, saltwater resistance, and resistance to chemicals used to sanitize swimming pool water; be usable by persons of varying sensitivity; and be usable with or without sunscreen.
In light of the foregoing, it is a first aspect of the present invention to provide a multilayer device which can be used to indicate the amount of exposure to sunlight. This aspect of the present invention is achieved by a multilayer sunlight dosage indicator comprising (a) an indicator layer comprising a sunlight-sensitive ink, wherein the ink undergoes a color change upon exposure to a known amount of sunlight; and (b) an overlayer comprising an amount of at least one UV absorber.
Another aspect of the present invention is to provide a method for indicating the amount of exposure to sunlight. This aspect of the present invention is achieved by providing a multilayer sunlight dosage indicator comprising (a) an indicator layer comprising a sunlight-sensitive ink, wherein the ink undergoes a color change upon exposure to a known amount of sunlight; and (b) an overlayer comprising an amount of at least one UV absorber, wherein the color change indicates exposure to a known amount of sunlight.
A further aspect of the present invention is to provide a method for adjusting the sensitivity of the sunlight dosage indicator. This aspect of the present invention is achieved by (1) providing a multilayer sunlight dosage indicator comprising (a) an indicator layer comprising a sunlight-sensitive ink, wherein the ink undergoes a color change upon exposure to a known amount of sunlight; and (b) an overlayer comprising an amount of at least one UV absorber, and (2) selecting the amount of UV absorber to alter the amount of sunlight necessary to cause the ink to change color.
Other aspects of the present invention, as well as the advantages thereof over existing prior art forms, will become apparent from the following brief description considered and interpreted in view of the accompanying drawing, and are accomplished by the improvements hereinafter described and claimed.